Relaying system



Sept. 14, 1948. 5, LENEHAN 2,449,490

RELAYING SYSTEM Filed June 16, 1945 WITNESSES: INVENTOR fiernandflene/vafl.

ATTORN EY Patented Sept. 14, 1948 RELAYING SYSTEM Bernard E. Lenehan, Bloomfield, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application June 16, 1945, Serial No. 5%,832

6 Claims.

My invention relates to other uses functions of a carrier-current relaying system for protecting transmission-lines against faults, said other uses functions being carrier-current functions other than transmission-line protection, and usually meaning telemetering or voice-communication control, or both, although there are many other other uses to which protective-relay carrier-current equipment is put, during normal fault-free line-conditions.

There are two principal objects of my invention. One is to provide double plate-keying, for startin the carrier-current transmission by closing, or making effective, the plate-circuit of the oscillator, one keying-circuit being for the protective relays, and the other for telemetering, and preferably also for the voice-control circuit, with high isolating plate-resistors whereby the telemetering keyer is separated from the relaying functions without requiring continuously energized relaying-circuits or excessive current on the telemetering contacts. I use the term keying broadly, in a sense covering electronic control, as well as mechanically moving contacts.

Heretofore, the preferred carrier-current control-means has been the cathode-circuit control, in which the telemetering and relaying contacts have been connected in parallel with each other, and in series with the relaying carrier-stop contacts, in the cathode-circuits of the carrier-current oscillator-tube and the carrier-current power-amplifier tubes, utilizing the 12-volt arcdrop in the cathode-circuit brealocontacts to impose a, 12-Volt negative bias on the tubes, particularly on the heavy-current amplifier-tubes, thereby reducing the burden on the break-contacts, as set forth in a patent granted to S. L. Goldsborough and myself, No. 2,255,934, granted September 16, 1941.

The telemetering contacts must, in effect, make and break a circuit with considerable rapidity, and for long periods of operation, resulting in millions of operations. Heretofore, in any practically successful circuits which could be devised, not counting certain circuits requiring complications which are frequently undesirable, these telemetering contacts have controlled all of the tubes in the transmitter, and have also carried additional current which flowed through series resistors of the relay coils, these burdens being imposed by reason of the necessity for giving preferential control to the protective relays. My new double plate-keying avoids this difficulty.

The second principal object of my invention is to provide a fault-responsive means for YEmOV-I ing the additional negative bias which is commonly placed on the powenarnplifier grids for the purpose of allowing the power-amplifier tubes to operate on the linear portion of their curve, for voice-modulation, thereby reducing the transnutter-output, sometimes to about half of its normal value. .Heretofore, when a fault occurred while the carrier-current apparatus was being utilized for voice-communication, the control of the starting and stopping of the carrier has been taken over by the protective relays, but no sufiiciently economical and practical means has been available for restoring the transmitter-output to its full value, under such circumstances. Hence, the relaying has been accomplished with the reduced output of the transmitter, a sufficiently wide margin of safety being allowed to make this possible. It is obviously advantageous, however, to restore the full transmitter-output, under these circumstances, and I have now been able to accomplish this purpose in a practical set.

With the foregoing and other objects in view, my invention consists in the systems, circuits, apparatus, combinations, methods, and parts, hereinafter described and claimed, and illustrated in the accompanying drawing, the single figure of which is a somewhat simplified diagrammatic view of circuits and apparatus illustrating my invention in an illustrative form of embodiment.

In the drawing, my invention is illustrated as being applied to the protection of a S-phase (SO-cycle transmission-line section I, having phases A, B, and C. The line-section I is connected to a bus 2 through a circuit-breaker 3, having an auxiliary make-contact 3a, and having a trip-coi1 TC.

The usual, or any desired, protective relays are provided, having alternating-current circuits which are shown diagrammatically, in a box 4, as being energized from a line-voltage potentialtransformer 5 and a line-current transformer 6. These protective relays are preferably of the instantaneous variety, and they include a set of directional elements, which are shown at DA, DB, DC, and DO, for the three line-phases and for ground-currents or zero-sequence currents, respectively. The protective relays are also illustrated as comprising two sets of distance-relays and ground-current relays, corresponding roughly to the second and third zones of distance-response, reaching out to seconcbzone faults, which are located beyond the far end of the protected line-section i, and to third-zone faults which are still more remote. The two zones of distanceresponses are indicated by the numerals 2 and 3, the phase-fault distance-elements being indicated as being of the impedance-type or modified-impedance type, as indicated by the letter Z, while the ground-fault fault-detector elements are indicated as overcurrent residual-current relays of different sensitivities, as indicated at 102 and I03. The impedance elements are designated as ZZA, Z213, ZZC, Z3A, 23B, and 23C for the various line-phases and distance-zones. The same letters and numerals of designation are applied to the various relay-contacts, which are shown elsewhere on the drawing, in the various direct-current circuits, which are shown in the form of an across-the-line direct-current diagram. The physical connections between the separated parts of the various relays are also symbolically indicated by arrows. The relays are shown in their deenergized positions.

My present invention concerns the control and operation of carrier-current apparatus, which is shown as comprising a transmitter T and a receiver R. The transmitter T comprises a masteroscillator tube OSC, and two amplifier-tubes AI and A2. The receiver R comprises a receiver detector-tube REC. The output-circuits of the power-amplifier tubes AI and A2, and the control-grid circuit of the receiver-tube REC, are coupled to a coupling transformer TI which is connected, through a line-tuner inductance Ll and a coupling capacitor CI, to one of the phaseconductors of the line I, said phase-conductor being provided with a line-trap LT for confining the radio-frequency carrier-currents to that lineconductor. The usual drain-coil L2 is provided, and also other refinements which are not shown on the simplified diagram of my drawing.

The oscillator OSC is rovided with a cathodecircuit I, a plate-circuit 8, and a control-grid circuit 9. Preferential carrier-stopping control is given to the protective relays by means of two back-contacts CSG and CSP, which normally connect the oscillator cathode-circuit 'l to the negative battery-terminal This is in accordance with the cathode-circuit control-system of the aforementioned Patent No. 2,255,934. The relays CSG and CSP are auxiliary directionally responsive ground-fault and phase-fault relays, respectively, which are provided with correspondingly lettered actuating-coils CSG and CSP, which are shown near the top of the direct-current connections of the drawing. Thus, the CSG-coil is energized in a circuit traceable from the positive battery-terminal through the DO ground-directional make-contact and the I02 ground-fault make-contact, to a directional ground-fault-circuit II, and thence through the CSG-coil to the negative battery-terminal The CSP-coil is energized from a directional phase-fault relaying-circuit I2, which is energized from any one of three circuits, corresponding to the three line-phases, each energizing circuit comprising a directional element, such as DA, and a second-zone impedance-element of the same phase, such as that indicated at 22A.

The illustrated relaying-system utilizes ground-fault preference, which was provided by means of a CSG make-contact, which is connected in parallel with the CSP back-contact, as indicated at I3, which will be well understood by those skilled in the art.

The oscillator grid-circuit is connected to the negative battery-terminal through a gridleak resistor GLO, and it is also connected to a tuned circuit I4, which includes a variometer L3 and three capacitors C2, C3, and C4. This tuned circuit is also connected to the oscillator platecircuit 8 through a blocking capacitor C5. This tuned circuit is further connected to the amplifier control-grid circuits 2| and 22 through blocking capacitors C5 and C1. The amplifier control-grid circuits 2| and 22 are connected, through grid resistors GLI and GL2, to a common amplifier grid circuit 23, which will be subsequently referred to.

The two amplifier cathode-circuits are connected together, as indicated at 24, and thence are connected, through a cathode-drop resistor RI, to the oscillator cathode-circuit I. The cathode-resistor RI thus makes the power-amplifier cathode-circuit 24 normally operate at a potentiol which is more positive than the negative bus by the voltage-drop in the cathode-resistor RI.

The oscillator plate-circuit 8 receives its direct-current energization through a radio-frequency choke-coil RFC, which connects the platecircuit 8 to a positive plate-supply circuit 25.

According to one feature of my present invention, a double plate-circuit, or two parallel connected plate-circuits 25a and 251), are utilized to energize the plate-supply circuit 25. The first branch plate-circuit 25a is connected, through a resistor Ra, to a relaying carrier-start circuit or bus 25. The second branch plate-circuit 25b is connected, through a resistor Rb, to a telemetering carrier-start circuit 21.

The relaying carrier-start circuit 26 is connected to the ositive bus through any one of five circuits containing the five normally open contacts, as follows, namely, the four make-contacts of the sensitive protective relays Z3A, Z3B, Z30, and 103, and a test push button PB which can initiate carrier-current transmission for testpurposes. The carrier-starting relay-contacts Z3A, Z3B, Z3C, and I03 are each provided with a serially connected operating coil of the corresponding one of the relays KA, KB, KC, and KG, respectively, which are utilized for other relaying purposes which are not shown on the drawing, because said other relaying purposes do not relate to the carrier-current control toward which my present invention is directed. The pushbutton contact PB has a small serially connected 28-ohm resistor R2, which is for the purpose of preventing the short-circuiting of any of the auxiliary relay coils KA, KB, KC, and KG which may happen to be energized at the time when the push button is depressed.

The telemetering carrier-start bus 21 is energized from a circuit 29, and thence, through a back-contact K3, from the positive bus by either one of two circuits, one being the telemetering contacts (or other telemetering control-means), which are diagrammatically indicated at TM, and the other being the make-contacts KI of a voice-communication relay KI which will be subsequently described.

The receiver-tube REC has its cathode-circuit 30 energized from a potentiometer 3| which is connected across the battery-terminals and The plate-circuit 32 of the receiver REC is connected to the positive battery-terminal through a milliammeter or other telemetering device 33, and a receiver-relay holding-coil HRH. The receiver-relay also has an operating or tripping coil RRT, which is shown in the top quarter of the diagram, in a shunt-circuit connected across the carrier-stopping back-contacts CSG and CSP, so that the receiver-relay is enerenema-o gized whenever carrier-current transmission Is stopped by a-relaying operation, but the receiver-- relay cannot respond to its operating or trippingcoil RRT, until carrier-current is no.- longcr received from the far-end line-terminal or terminals', at which time the receiver-relay holdingcoil RRH ceases to be energized from the receiver-tube REC, and the receiver-relay then operates to close its two: make-contacts RR, which are utilized to connect the directional relayingcircuits H and 12, respectively, to the trippingcircuit 35 for trippin the circuit-breaker 3 through a circuit which includes the breakercontact 3a, and the trip-coil TC.

Since the receiver-relay tripping-coil RRT is connected in shunt across the carrier-stopping back-contacts CSG and CSP, it is also connected between the oscillator cathode-circuit l and the negative battery terminal This coil RRT has a moderately high resistance, or it has a resistor R3 connected in series with it. The oscillator cathode-circuit I is also connected to the relaying carrier-starting circuit 25, through a still larger resistor R4, which cooperates with the resistor R3 to constitute a voltage-divider which prevents the oscillator OSC from oscillating whenever the relaying carrier-stopping cathode-circuit is opened at either the CSG or CSP back-contacts.

The relaying carrier-start circuit 26 is also utilized for other purposes. In order to provide sufficient current for energizing the auxiliary relays KA, KB, KC, or KG, as the case may be, it is necessary to connect the relaying carrier-start bus 26 to the negative battery-terminal through a circuit of fairly low resistance, as indicated by the resistor R5. It is also desirable to energize the coil of the auxiliary relay K3 whenever the relaying carrier-start circuit 26 is energized from the positive bus and this K3 energization is diagrammatically indicated by including the operating coil of the relay K3, in series with the resistor R5, between the neg ative bus and the relaying carrier-start bus 26.

The carrier-current apparatus may be utilized for voice-communication, as by means of a handset microphone 36, which is shown connected from the negative bus through a voice-communication control-button V0 to a relaying-circuit 31, and thence to the operating coil of the auxiliary relay Ki, and a resistor R6, which is connected to the positive bus Connected across themicrophone 35' and the voice-control push button V0 is the primary winding 38 of a transmitter modulating microphone-transformer T2, in a circuit which also includes an isolating capacitor C8.

The auxiliary voice-communicating relay Kl has two contacts which are shown on the drawing. One of these contacts is the previously mentioned make-contact Kl which is utilized as one of the paths for energizing the telemetering carrier-start circuit 2'5. The other Kl contact is a back-contact, also marked Kl, which is utilized to connect the amplifier grid-biasing circuit 23 to the negative battery-terminal at all times except when the voice-communication push button V0 is being held depressed while the operator, at the illustrated transmitter T, is speaking into the microphone 36 The mod'ulation-transformer T2 has a secondary winding 39, which is connected between the. grid-biasing circuit 23 of the amplifiers AI and A2 and an intermediate circuit 4|, which is 6 connected; through a grid-leak resistor GL3, to the grid-circuit 9 of the oscillator-tube 080; The intermediate circuit 4| is also connected, through a; grid-capacitor C9, to the negative battery-terminal G)'..

In accordance with my invention, the potential of the amplifier grid-biasing circuit 23 is also controlled by means of aresistor Re, which is connected between said grid-biasing circuit 23 and the. relaying carrier-start. circuit 26, so that the R0 resistor-connection is made, in the gridcircuit, in the same moment asthe carrier-starting operation of the relays.

Associated with the handset microphone 36, is also a handset receiver 42, which is energized from the secondary winding 43 of an audio-frequency receiver-transformer T3, the primary winding 44 of which: is coupled to the plate-circuit 32 of the receiver-tube REC, through a capacitor CID.

The particular carrier-current system which is shown in the drawing is also provided with sleet-testing apparatus, as is quite common in such systems, for determining sleet-conditions on the protected line-sectionl, by noting the attenuation of the carrier-signal which is received from the remote line-terminal. To this end; as shown at the extreme bottom of the drawing, the apparatus is provided with a sleet-test push but ton ST, which energizes the operating coil K2 of an auxiliary relay K2, through a resistor R1. The auxiliary sleet-test relay K2 is provided with a back-contact K2 which is utilized to short out some or all of a receiver-circuit resistor R8; which is included in series with the receiver-circuit 45 which is tapped off from the couplingtrans-fcrmer Ti for energizing the receiver R. When the sleettest button ST is depressed, the relay K2. is energized, and opens its back-contact K2 which inserts some or all of the resistor R8 in this receiver 'circuit, thus causing the receiver-tube REC to operate on the straight portion of its opcrating-curve, instead of on a saturated portion thereof, so that the amount of attenuation can be judged by the reading of the milliammeter' 33, or other means.

The general operation of the sleet-detection apparatus is described and claimed in a Go1dsborough Patent No. 2,372,018, granted March 20-, 1945-, on an application Serial No. 468,229, filed December 8, 1942. For sleet-detection, the operator at the far end of the protected line-section is requested to depress his carrier-starting push button PB, thus transmitting carrier; then the operator at the receiving station depresses his sleet-test button ST and notes the milliammeter 33 reading.

The auxiliary relay K3, which responds to the energizatiorr of the relaying carrier-start bus 26, has two contacts which are shown on the drawing. One of these contacts is the previously mentioned back-contact K3 which is included in the telemetering branch platc-circuit 25b. The other contact of the auxiliary relay K3 is a makecontact K3 which is shunted around the receivercircuit resistance R8. A relay, such as K3, energized so as to be responsive to any energization of the fault-detector bus 2.6, has been known before,.but in a system in which the fault-detector bus was energized from the negative batteryterminal rather than the positive batteryterminal (4-) as shown, for example, in a patent to J. L, Blackburn and J. F. Chapman, No. 2,367,921, granted January 23-, 1945.

In the oscillator circu-its, a capacitor OH is connected between the positive terminal 25 of the plate-choke RFC and the cathode-circuit l, for the purpose of providing a radio-frequency impedance which is low, as compared to the impedances of the plate-resistors Ra and Rb and the various other circuits which are connected to the carrier-start buses 26 and 21. In this way, I reduce, to a negligible amount, any change in the oscillator-frequency, as a result of changing over from one plate supply-circuit 25a or 251), to the other.

In the power-amplifier circuits, a capacitor CI2 is connected in shunt across the cathode-resistor RI, that is, it is connected between the amplifier cathode-circuits 24 and the oscillator cathodecircuit 1. This capacitor CI2 servesto suppress parasitic oscillations which might otherwise tend to occur because of the continuous energization of the amplifier-tubes Al and A2.

While I have described the illustrative equipment at only one terminal of the protected linesection I, it will be understood, of course, that the same, or similar, equipment will, or may, be provided at the other terminal or terminals of the protected line-section.

In operation, the oscillator-tube 080 is normally unenergized, while the power-amplifier tubes Al and A2 are normally energized, which is a new feature. Under these circumstances, the carrier-current transmitter T is not transmitting, because oscillations are not being generated by the oscillator-tube OSC.

One of the important features of my invention is the provision of two branch-circuits, connected in parallel, as shown at 25a and 25b, for supplying the oscillator-tube OSC with direct-current energization. These parallel-connected branch energizing-circuits 25a and 25b are advantageously connected, as shown, in the plate supplycircuit 25 of the oscillator, as such connection l facilitates the grid-circuit connections, but it is conceivably possible for these branch supplycircuits 25a and 25b to be placed in either the cathode tube-circuit 1 or the anode tube-circuit 25. A feature of the two branch supply-circuits 25a and 25b is that each circuit includes a rather considerable resistance, Ru. and Rb, respectively.

While I am not limited, of course, to any particular values of resistances, it may help to fix our ideas by noting illustrative values of the various resistances on the drawing. Thus, the double plate-resistors Ra and Rb are each marked as being 3000 ohms, in the particular illustrative example of my invention which is shown in the drawing.

An important function of these branch-circuit plate-resistors Ra and Rb is to substantially isolate the telemetering keyer TM from the relaying-circuits which are connected to the relaying carrier-start bus 26, so that the rapidly and continuously operating telemetering contacts TM do not have to carry any substantial added burden, by reason of the parallel connection of the protective-relaying carrier-starting contacts such as 23A, 23B, Z30, or I03.

Thus, when the telemetering contact TM closes, direct-current plate-current for the oscillatortube 080 flows through the telemetering branchcircuit resistor Rb, producing a voltage-drop therein, and thus applying a certain fraction of the battery-voltage to the plate-supply circuit 25 of the oscillator. Connected in parallel with the oscillator-tube OSC, starting with the plate-supply circuit 25, is a tube-shunting circuit 25aRa- 26--R5, which is connected to the negative bus through the K3-coil. By reason of the high resistance of the other branch-circuit resistor Ra, this parallel-connected circuit draws only a relatively small current-(too small to actuate the relay K3)in addition to the current which is drawn by the oscillator-tube OSC through the radio-frequency choke-coil RFC, the plate-circuit 8, and the cathode-circuit 1. Thus, the burden on the telemetering contact I'M is substantially only the necessary burden of the direct-current supply for the oscillator-tube 030.

It will be noted that this reduction in the burden on the telemetering contact TM is very important, because of the millions of operations which said contact is called upon to make. It will be further noted that my double plate-keying system has accomplished this reduction in the burden on the telemetering contact TM, without requiring continuously energized relaying-circuits, or other disadvantageous features.

A still further reduction in the burden on the telemetering contacts TM is accomplished by utilizing said contacts to key only the direct-current energizing-current of the oscillator-tube OSC, without having to key the much larger energizing-currents of the two, four, or six power-amplifier tubes Al and A2, only two such tubes being illustrated. I accomplish this by normally continuously energizing the power-amplifier tubes Al and A2 with direct-current supplied from the battery-terminals and the plate-circuit energization being shown in a connection 46 from the positive bus to the midpoint of the primary winding 41 of the coupling-transformer TI, and thence directly to the plates of the amplifier-tubes Al and A2.

As previously stated, the amplifier cathodecircuit capacitor C|2 serves to considerably reduce the likelihood of unwanted parasitic oscillations which might possibly occur, as a result of the normal continuous energization of the amplifier tubes AI and A2, during periods when the oscillator-tube OSC may have its plate-circuit 25 opened.

In the event of a fault on the transmissionsystem |2, one or more of the fault-detectors Z3A, Z3B, Z3C, or I03 will respond, energizing the relaying carrier-start circuit 26, and thence energizing the relaying branch plate-circuit 25a. of the oscillator-tube OSC, and at the same time energizing the auxiliary relay K3, which opens its back-contact K3 in the telemetering branch plate-circuit 25b, and closes its make-contact K3 around the receiver-circuit resistor R8. Thus, the telemetering contact TM and the parallel connected voice-communication relay make-contact Kl are both rendered inoperative by the opening of the K3 back-contact, while the K3 make-contact in the receiver-circuit 45 insures maximum energization of the receiver-tube REC, so that the latter operates in a saturated condition, largely insensitive to attenuation, even though the station-operator might, at that moment, be in the act of making a sleet-test by depressing the sleet-test button ST, and thus energizing the sleet-test relay K2, the back-contact of which inserts most or all of the receivercircuit resistance R8, which is thus shorted out, again, by the relaying-responsive auxiliary relay K3.

As previously noted, any material change in the carrier-current frequency, depending upon which one of the two plate keying-circuits 25a or 251) is energized, is minimized by the provision of the capacitor CH of the oscillator-circuit.

The particular carrier-current relaying-sys-- tem which is illustrated in the drawing is of a type in which, as. previously described, it is necessary for the carrier-current transmission to be interrupted at both or all terminals of the protected line-section I", in order to deenergize the receiver-relay holding-coil RRH, which permits the receiver-relay tripping-coil RRT to actuate the receiver-relay and close its two make-contacts RR and BE, in the two tripping-circuits which are responsive, respectively, to the ground-fault and phase-fault directional relaying'buses H and I2, shown near the top of the figure. To this end, it is necessary forthe relaying carrierstopping contacts CSG and CSP to have complete control over the stoppage of carrier-current transmission, regardless of what carrier-starting contacts may be closed, whether the relaying;

carrier-start contacts 23A, 23B, Z3C, 103, or PB, or the telemetering contacts TM, or the voicecommunication make-contact Kl.

It is accordingly necessary for the relaying carrier-stop contacts CSG and CSP to be included somewhere in the direct-current energizationcircuits of the oscillator-tube OSC, as by being placed either in series with the common platesupply circuit 25, or the plate-circuit 8', or the cathode-circuit I, or otherwise, as by biasing the control-grid 9, or detuning or interrupting one of the essential tuned circuits or output-circuits of the oscillator-tube 080. In the particular system illustrated in the drawing, the cathodecircuit carrier-stopping connection is shown, because of certain inherent advantages therein, but it is to be understood that I am not limited to this particular showing.

In the illustrated system, the relaying carrierstopping contacts CSG and CSP are also included in series with the cathode-circuits 24 of the amplifier-tubes Al and A2, so as to altogether deenergize said amplifier-tubes at all times when the protective relays call for a stoppage of carriercurrent transmission, thus taking no chances of parasitic transmitter-oscillations during an instant when it is necessary to be absolutely sure of an interruption of carrier-current transmission in order to obtain a correct tripping-operation of'the line circuit-breal er 3. The inclusion of the relaying carrier-stopping contacts CSG and CSP in series with the cathode-circuits I and 24 of the transmitter-tubes, while the grid-potential circuits are coupled back to the negative bus is advantageous in providing an additional 12-volt negative bias on the grid-circuits 9 and 23, as a result of the l2-volt arcing-voltage which appears across the carrier-stopping contacts CSG or CSP, when they open, in the process of interrupting the cathode-currents of the transmitter-tubes, as described and claimed in the aforesaid Patent 2,255,934.

Another important feature of my invention has to do with the ease in which the carrierequipment may be utilized, at times, for voicecommuniqation. :Since practically all carriercurrent relaying equipment is arranged for voicecommunication, this is an important. feature of my invention. )When voice-communication is utilized, it is customary to provide a voice-control button VC, which must be depressed in order to initiate carrier-current transmission, and it must be held depressed in order to main? tain such transmission during the time when the operator is speaking into the microphone 35. Inorder to efiect voice-modulation of the carrier-current transmitter T, it is necessary, for all practical purposes, to cause the power-ampli-' fier tubes Al and A2 to operate on the linear portion of their curve, instead of operating in a more or less saturated condition. To this end, it has been customary to utilize the KI backcontacts of the voice-communication relay Kl, which is energized whenever the voice-control button VC is held down.

Ordinarily, when the carrier set is not being utilized for talking, the KI back-contact is closed, connecting the amplifier grid-biasing circuit 23 directly to the negative bus This imposes a certain small negative bias on the amplifier tubes AI and A2, said bias being equal to the voltage-drop in the cathode-resistor RI of the amplifier-tubes. This small normal negative bias on the amplifier-tubes is sufficient to reduce the amplifier grid-currents to a small value, and to cause the amplifier-tubes Al and A2 to operate at their maximum output, which is desired for relaying, and for some types of telemetering, as in the illustrated system.

When voice-modulation is being utilized, it is necessary to increase the negative bias on the amplifier grid-biasing circuit 23. There are various means available for accomplishing this purpose. The particular system which is illustrated in the drawing makes use, for this purpose, of the negative bias which appears on the control-grid circuit 9 of the oscillator-tube 050, while the latter is oscillating, this negative bias being produced by the rectification of a small portion of each cycle of the carrier-frequency component of the grid-voltage, by the rectifying action of the grid and cathode, operating, respectively, as the plate and cathode of a rectifiervalve.

When the voice-communication relay Kl is energized it opens its back-contact Kl, disconnecting the amplifier grid-biasing circuit 23 from the negative bus and causing it to be connected to the still more negative oscillator gridcircuit 9, through the secondary Winding 39 of the modulator-transformer T2, and the additional grid-leak resistor GL3. At the same time, the grid-capacitor C9 is made effective, in the amplifier grid-circuits. The effect of this change, in the amplifier grid-control is to put the amplifier-tubes Al and A2 in a proper condition for voice-modulation, at the same time reducing the carrier-current output of the amplifier-tubes Al and A2. This power-output reduction may be either of a rather small amount, or it may be quite considerable, amounting to about half of the maximum carrier-current output, depending upon the nature of the carrier-current apparatus,

Heretofore, if a transmission line-fault should occur at a time when the station-operator was speaking over the microphone 36, this reduced carrier-current output of the transmitter T was perforce tolerated, for lack of any known, sufficiently economical and practical way of instantaneously restoring the full power-output of the amplifier-tubes. Heretofore, reliance was placed upon a rather generous margin of safety, which was always provided, in order to make ample allowances for unusual attenuation-conditions, and for badly deteriorated tubes. It has been obviously desirable, however, to correct this reduced-output condition, if a relaying controloperation should become necessary during voicecommunication; but the means for correcting this evil have not been readily available, because the relaying carrier-starting circuit 2% has not 11 previously been included in the plate-circuit of the oscillator-tube 080.

An important advantage of that phase of my invention which includes putting the relaying carrier-start circuit 26 in a plate-supply circuit 25a of the oscillator-tube CS0, is that it provides a means, readily available, for removing the extra negative grid-bias from the amplifier gridbiasing circuit 23, if a fault occurs at a time when the voice-communication back-contact Kl is open. To accomplish this purpose, all that is necessary is to connect my grid-control resistor R between the amplifier grid-biasing circuit 23 and the relaying carrier-start circuit 25.

Assuming that the voice-control back-contact Kl is open, this additional grid-control resistance Rc cooperates with the auxiliary grid-leak resistance GL3 in providing a, potentiometer between the oscillator grid-cirouit 9, which is more negative than the negative bus and the positive bus of the station-battery. The relative magnitudes of the resistors GL3 and Re are such as to restore the amplifier grid-biasing circuit 23 to substantially the potential of the negative bus thus restoring the full power-output of the amplifiers Al and A2. When the voicecommunication back-contact Kl is closed again, the amplifier grid-biasing circuit 23 is held, by said KI back-contact, absolutely at the potential of the negative bus so that the additional grid-biasing resistor He has no effect. Of course, even when the fault-detector bus 26 is not energized, during voice-modulation, the grid-biasing circuit 23 is connected to the positive bus through a circuit including Re, 26, Ra, 25a, 25b, Rb, the K3 back-contact, the telemetering carrier-start bus 21, and the Kl make-contact, but the added resistance of the two large resistances 25a and 26a makes the potential of the controlled grid-bias circuit 23 appreciably more negative than when the energization of the faultdetector bus 26 cuts out said two resistors 25a and 25b.

While I have illustrated my invention, and described its mode of operation, in particular reference to a single illustrative form of embodiment, I wish it to be understood that many changes in details and arrangement are possible, as the various features of the invention are applicable to diiferent kinds of carrier-current protective relaying-systems, which are also used for another use or uses, other than transmission-line protection. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language.

I claim as my invention:

1. A plural-purpose carrier-current relayingsystem for protecting a transmission-line section, and also at times performing a function other than protecting the line section, said system comprising a carrier-current transmitter comprising an oscillator-tube having a cathode tube-circuit and a plate tube-circuit for supplying said oscillator-tube with direct-current energization, one of said tube-circuits comprising two branch-circuits connected in parallel, each branch-circuit including a considerable resistance, relaying carrier-start contact-means in series with one of said branch-circuits, control-means for said other function in series with the other branch circuit, and a relay-circuit path of relatively low resistance in series with the relaying carrier-start contact-means and in shunt to said oscillator tube.

2. A plural-purpose carrier-current relayingsystem for protecting a transmission-line section, and also at times performing a function other than protecting the line-section, said system comprising a carrier-current transmitter comprising an oscillator-tube having two parallelconnected branch plate-circuits for supplying said oscillator-tube with direct-current energization, each branch-circuit including a considerable resistance, relaying carrier-start contact-means in series with one of said branch-circuits, controlmeans for said other function in series with the other branch-circuit, and a relay-circuit path of relatively low resistance in series with the relaying carrier-start contact-means and in shunt to said oscillator-tube.

3. A plural-purpose carrier-current relayingsystem for protecting a transmission-line section, and also at times performing a function other than protecting the line-section, said system comprising a carrier-current transmitter comprising an oscillator-tube having a cathode-circuit, normally closed relaying carrier-stop contacts in series with said cathode-circuit, said oscillator-tube also having two parallel-connected branch platecircuits for supplying said oscillator-tube with direct-current energization, each branch-circuit including a considerable resistance, relaying carrier-start contact-means in series with one of said branch-circuits, control-means for said other function in series with the other branch-circuit, and a relay-circuit path of relatively low resistance in series with the relaying carrier-start contact-means and in shunt to said oscillator-tube.

l. A plural-purpose carrier-current relayingsystem for protecting a transmission-line section, and also at times performing a function other than protecting the line-section, said system comprising a carrier-current transmitter comprising an oscillator-tube and amplifier-tube means having a common cathode-circuit, normally closed relaying carrier-stop contacts in series with said common cathode-circuit, said amplifier-tube means having a normally continuously energized plate-circuit connection, said oscillator-tube having two parallel-connected branch plate-circuits for supplying said oscillator-tube with direct-current energization, each branch-circuit including a considerable resistance, relaying carrier-start contact-means in series with one of said branchcircuits, control-means for said other function in series with the other branch-circuit, and a relaycircuit path of relatively low resistance in series with the relaying carrier-start contact-means and in shunt to said oscillator-tube.

5. A plural-purpose carrier-current relayingsystem for protecting a transmission-line section, and also at times performing a voice-modulation function, comprising a carrier-current transmitter comprising an oscillator-tube and amplifiertube means, said transmitter including a plurality of grid-biasing means for biasing a controlled grid-circuit at different biases, including a normal grid-bias circuit-connection and a more negative grid-bias connection, circuit-means for supplying plate-circuit and cathode-circuit directcurrent energization to said oscillator-tube and said amplifier-tube means, voice-modulation control-means for interrupting aid normal grid-bias circuit-connection and rendering said more negative grid-bias connection eflfective, an additional grid-biasing resistor, and relaying transmittercontrolling means for controlling the transmitter in accordance with a protective relaying function, said relaying transmitter-controlling means including fault-responsive circuit-means for efiec- 13 tively connecting said additional grid-biasing resistor between said controlled grid-circuit and a source of more positive potential for restoring said controlled grid-circuit to its normal potential.

6. A plural-purpose carrier-current relayingsystem for protecting a transmission-line section, and also at times performing a voice-modulation function, comprising a carrier-current transmitter comprising an oscillator-tube and amplifiertube means, said transmitter including a plurality of grid-biasing means for biasing a controlled grid-circuit at different biases, including a normal grid-bias circuit-connection and a more negative grid-bias connection, circuit-means for supplying plate-circuit and cathode-circuit directcurrent energization to said oscillator-tube and said amplifier-tube means, said oscillator-tube having two parallel-connected branch plate-circuits, each branch-circuit including a considerable resistance, relaying carrier-starting means in series with one of said branch-circuits, voicemodulation carrier-starting means in series with REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 0 2,255,934 Lenehan et a1 Sept. 16, 1941 2,372,078 Goldsborough Mar. 20, 1945 2,387,146 Haberl Oct. 16, 1945 

